Method of making flint clay brick



Sept 27, 1938- R. P. HEUER ET A1. 2,131,252

` METHOD OFMAKING FLINT CLAY BRICK Filed April s, 1957 Jaffaaf-M-M `Patented Sept. 27, 1938 UNITED STATES 2,131,252 METHOD OF MAKING FLINT CLAY BRICK Russell P. Heuer, Bryn Mawr, and Alex Edward Fitzgerald, Merion, Pa., assignors to General Refractories Company,

Philadelphia, Pa., a

corporation of Pennsylvania Application April 3, 1937, Serial No. 134,828

Claims.

The present invention relates `to dense refractory brick made from hard flint clay and to methods of producing such brick.

A purpose of the invention is to produce iiint clay brick of higher refractoriness, bulk specic gravity and cold crushing strength, and lower reheat shrinkage, spalling loss and manufacturing loss than the iint clay brick of the prior art, securing some or all of the followingv properties: an alumina content in the finished brick in excess of 42% (a measure of refractoriness), a bulk specific gravity in excess of 2.38, a cold crushing strength above 1200 pounds per square inch (84.4 kilograms per square centimeter), a linear change when reheated at 1600 C. (2912 F.) of

not more than 1%, a spalling loss after having been preheated to 1650 C. (3002 F.) of not more than 1%, a linear ring shrinkage of less than 9% and a manufacturing loss of less-than A further purpose is to produce a higher quality iiint clay brick notwithstanding the inevitable high shrinkage which takes place in kiln ring.

A further purpose is to mix raw hard int clay, having an alumina contentof 35% to 45%, with 2% to 5%, preferably 3%, of bentonite or similar highly colloidal clay and substantially no calcined int clay or grog (certainly less than 5%), to employbetween 30% 4and 70% of particles between 3 and 28 Tyler standard mesh per linear inch (1.4 and 118.4 mesh per square centimeter) and between 70% and 30% of particles below 48 Tyler standard mesh per linear inch (357.1 mesh per square centimeter), to prepare the mix on a special pan, to mold with a molding eiiciency in excess.Y of 90% and to fire at a minimum temperature of one pyrometric cone below the temperature producing maximum l bulk specific gravity when firing lumps ofthe particular int clay.

A further purpose is to fire low burning Missouri hard flint clay at one maturing temperature and to fire high burning Missouri hard flint clay at another and higher maturing temperature.

Further purposes appear in the specification and in the-claims.

The figure shows curves useful in explaining the invention.

In the past eiorts have been made to produce iiint clay brick of improved properties from hard iiint clay. Holmes and Paul, AJournal of the American Ceramic Society (1931) 755 to 763, by starting with hard lnt clayfrom the Missouri diaspore eld, bonding with bentonite, using -no grog, and ring at about cone 16, obtained brick which were unsatisfactory from the standpoint of reheating shrinkageA and apparently other properties.

'I'he present inventors have studied the problem of improving the properties of iiint clay brick, and have succeeded in obtaining flint clay brick of very satisfactory properties by using a somewhat different procedure from that employed by Holmes and Paul, and in some cases employing a different raw material.

The present invention is the result of an investigation made of the properties of clays of the Missouri eld. The invention is of course applicable to other clays. In this iield there are soft or semi-hard clays, hard flint clays and diasporitic clays. the firing shrinkage of the clay when molded into brick and the required tiring treatment to mnimize shrinkage during service are primary considerations in the selection of a satisfactory clay.

'Ihe present inventors have discovered that there are two distinct types of hard flint clays which necessitate distinctly different firing treatments as later explained.

Some of the properties of the various clays will be considered briey.

Hardness The soft or semi-hard clays exhibit the following hardness as indicated by the disintegration of the particles by washing:

Screen analysis in The' particle hardness of the hard int clays is as follows:

Screen analysis inA percentage Before washing washing 0n Tyler standard 3 mesh per linear inch screen i 0 0 On Tyler standard 6 mesh per linear inch screen 92 t0 97 60 to 90 It is evident that the hardness of the flint clays is markedly superior to that of the soft or semihard clays.

Refractoriness Refractoriness in clay is known to increase as the alumina vcontent increases and as the fluxes such as iron oxide and alkalis decrease. Typi- The refractoriness of the clay,l

After S ft Hard mn'i clay o or Semimard Dialroritic clay Low High y burning burning Ignition 1058-.--. 10 t0 12 12 to 14 12 t0 14 12. 5 to 14 30 to 35 35 to 45 35 t0 45. 63 t0 78 0.9t0 1.8 0.3t0 0.9 0.3t0 0.9 0.4t0 1.2 0.81:() 2.1 0.5120 1.1 0.5t0 1.1 0.7t0 1.8

The fusion point of soft or semi-hard clay is about cone 32 (3092 F., 1700 0.), while the fusion point of hard flint clay, whether high burning or low burning, is about cone 34 (3200 F., 1760 C.). The fusion point of diasporitic clay is about cone 38 (3335 F., 1835" C.).

It is obvious from the above that diasporitic clay is more refractory than either type of hard int clay, and that hard flint clay is morerefractory than soft or semi-hard clay.

Firing minimize Information as to firing shrinkage may be obtained from the drawing which shows curves for the firing characteristics of l soft or semi-hard clay, low burning and high burning flint clay and diasporitic clay. In the curves, the ordinates are bulk specific gravity and the abscissae are firing treatment in pyrometric cones.

These data for plotting the curves were obtained by determining the bulk specific gravities of lumps of the various clays which were fired or metric cones (The Edward Orton, Jr. Ceramic Foundation) and fired, the cone of the burn being noted. These lumps are crushed and pieces passing 6 Tyler standard mesh per linear inch but remaining on 8 Tyler standard mesh per linear inch are selected for testing. These are dried to constant weight and their weight (M) is noted. 'I'hen they are boiled in water for one hour. After boiling the wateris decanted and -thepieces are freed of surface water by rubbing them around lightly with the fingers on a 10 Tyler standard mesh per linear inch screen which rests on a dry cotton towel until the surface water is removed. When properly treated the pieces no longer adhere to each other. These pieces n ow free of surface water are then put in a graduated burette partially lled with water and the volume of water (V) which is displaced is determined. The bulk specific gravity of the pieces under examination is obtained by the formula:

Bulk specific gravity=g 'Ihis method is accurate to within 2%.

can be drawnand the temperature at which theA clay attains maximum bulk speciflcgravity determined.

76 At the extreme left of the iigure, the bulk speciiic gravities of the clays as they come from the mine are indicated, along with the corresponding bulk specific gravities on a dehydrated basis.

From the curves it is possible to determine the amount of shrinkage which will occur when a given raw clay is fired sufficiently to remove all shrinkage. If we consider soft or semi-hard clay having a bulk specific gravity as mined of 2.40

semi-hard clay, it is seen that the maximum bulk specific gravity attained is 2.52. The increase in bulk specific gravity due to firing, 2.52--214, represents a volume shrinkage of 1,5% or a linear shrinkage of about 5%, within the safe range of commercialpractice. At the .present time some soft or semi-hard clay mixes which exhibitlinear firing shrinkages of about 7% are manufactured into brick.

Calculating on the same basis, the hard int clay of either the low burning or high burning type contains about 13% of chemically combined water and has a bulk specific gravity on the dehydrated ba'sis of 1.97 or 1.96. The maximum bulk specific gravity attained by firing is 2.69 and the linear shrinkage is about 9%. Although this is a high linear shrinkage, compared to standard practice, it is within the range of commercial possibility.

Applying similar considerations to the diaspo ritic clay, it is found that the linearv firing shrinkage is above 11%, beyond any figure obtained for clays commercially handled.

In summary, therefore, it would appear that,

judging by firing shrinkages, the soft or semi-hard The curves in the gure throw considerable light on the firing treatment which may be successfully employed with the various clays. The curve for soft or semi-hard clay (in solid line) indicates that the maximum specific gravity and hence freedom from shrinkage are obtained by firing at about cone 11. In the case of the low burning hard flint clay (plotted in dotted line). the maximum specic gravity is reached by firing at about cone 12 or 13. For the high burning hard flint clay (plotted in dash-and-single-dotted line) the maximum speciiic gravity is attained at cone 17. The diasporitic clay (plotted in dashand-double-:dotted line) must be heated to at least cone 28 to attain a volume-stable condition.

The difference in firing characteristics between the low burning and high burning hard flint clays is an interesting discovery of the present inventors. 'I'he cause is not apparent, as the low burning and high burning harddiint clays have substantially the same chemical analyses even down to the minor constituents, the colloidal characters do not seem to differ and the change in screen analyses upon washing are virtually identical. 'I'he differences in proper firing treatments are so marked, however, that a firing treatment which would be proper for low burning hard flint clay proves to be entirely unsatisfactory for'high burning hard flint clay, while the fixing treatment for the high burning hard flint clay is unnecessary and an economic waste if applied to the low burning hard flint clay.

Of the clays just discussed, the hard int clays are the only ones which may be commercially employed as a major componentl in mixes used for the production of dense bricks of high refractoriness. The soft or semi-hard clays lack the refractoriness required if they are to be used in excess of 30% in the brick mixes and the diasporitic clays shrink excessively and cannot be fired to the necessary density in the present commercial equipment.

The investigations of the present inventors indicate that the hard iiint clays not only possess the required refractoriness, but that the firing shrinkage may be satisfactorily coped with, and the clays may be rendered volume-stable by the proper firing treatment. To manufacture a satisfactory brick from such hard int clays, it is important to take special precautions regarding bonding, grain sizing, mix preparationand molding, as well as ring.

After the hard int clay is mined, it should be ground and classified according to grain size and a mix prepared containing large particles and small particles, with a relatively small proportion and preferably an entire absence of intermediate sized particles.- The larger particles should be between 3 and 28 Tyler standard mesh per linear inch (1.4 and 118.4 mesh per square centimeter) and the smaller particles should be below 48 Tyler standard mesh per linear inch (357.1 mesh per square centimeter). 'Ihe proportions of larger and smaller particles should Abe from 30% to 70% of larger particles and from 70% to 30% of smaller particles.

The quantity of .particles between 28 and 48 Tyler standard mesh per linear inch (118.4 and age, for example about 2%, and high manufacturing loss.

The hardiiint clay is quite nonplastic. Failure to add a bond results in low cold crushing strength and high manufacturing loss. On the other hand, use of any considerable quantity of bond produces in the brick undesirable characteristics previously discussed in connection with soft or semi-hard clay, such as lack of refractoriness, 10W bulk density and high spalling loss. The

experiments of the present inventors indicate that the brick may be bonded satisfactorily by adding from 2% to 5% of bentonite or similar material, the preferable quantity being about 3%.

As materials similar to bentonite, ehrenbergite, montmorillonite, damorterolite and bidellite are recognized. All are characterized by very ne grain, very high colloid `content and high water absorption as compared with ordinary plastic or bond clays. Wherever bentonite is mentioned in the claims, it will be understood that these and other equivalents are included.

The presence of calcined clay or grog in the mix is very undesirable as it causes low bulk density, low cold crushing strength, high reheat shrinkage and high spalling loss. The brick containing a substantial quantity of calcined clay mixed with raw clay develops cracks on reheating.

In order to avoid these undesirable characteristics, it is preferred to eliminate the calcined clay entirely, and in any case the quantity of calcined clay in the mix should be 5% or less. It will thus be evident that the preferable mix will comprise 98% to 95% of hard fiint clay and.2% to 5% of bentonite, with between 30% and V70% of larger particles between 3 and 28 Tyler standard mesh per linear inch (1.4 and 118.4 mesh per square centimeter) and between 70% and 30% of smaller particles through 48 Tyler standard mesh per linear inch (357.1 mesh per square centimeter) The mix of properly sized hard flint clay particles and bentonite, in the proper proportions and with the proper amount of water, should be prepared so as to obtain uniform distribution of bentonite over the surfaces of the hard int clay particles. The ordinary batching does not produce the most desirable uniformity of batch and accordingly it is strongly recommended that a special pan or mixer such as 4th'e Simpson, Lan.- caster or Clearfield mixer be used (see for example Eirich and Eirich United States Patents Nos. 1,663,830; 1,728,598 and 1,737,301)

Poor batching may result in low bulk. density. For example, Where all other conditions were the same, hard fiint clay brick whose mix was prepared on a special pan had a bulk specific gravity called regular way, to 22% Where it was prepared in a special pan, and in another case from 32% Where the mix was prepared in a regular pan to 6% where it was prepared in a special pan. It is thus evident thatin manufacturing brick from hard int clay, the employment of a special pan has decided advantages.

The molding or pressing of the brick should be conducted` with a pressing efficiency in excess .of 90%. lBy pressing efficiency is meant the ratio on a percentage basis of the bulk specific gravity of thev green dry brick to the bulk specific gravity ofthe dry raw mix, the latter being calculated from the bulk specific gravity of the dry ingredients and their proportion by weight in the mix. To obtain such 'high pressing efliciencies it is ordinarily necessary to employ pressures in excess of 1000- pounds per square inch (70.3 kilograms per square centimeter) and preferably in excess of 5000 pounds per square inch (351.5 kilograms per square centimeter). It will be understood that it is preferable to use the pressing eiciency rather than the pressure a's the guide for pressing, as slight diierences in the raw material or in the mix preparation change the pressure requirements.

Pressing eiciency below 90% will result in low bulk specific gravity. For example a handmolded brick prepared and fired according to the .disclosure of the present invention had a bulk specific gravity for the green dry brick of only 1.97 and for the red brick of only 2.28. Likewise low cold crushing strength, high reheat shrinkage and high manufacturing loss result from low pressing eiliciency.

The brick of the present invention, after/moldfl u ing, are dried and then red in a commercial kiln. For best results the brick when set in the kiln should rest on a material having firing shrinkage approximately equal tothat of the brick. This is accomplished by eliminating the use of previously burned'brick in the setting and making the setting entirely of brick having the high ring shrinkage. The spacing between bricks set in the may seriously impair or destroy the quality of the K after such treatment;

same area in the kilnshould be uniform. The

gas .velocity through the spaces between the' bricks should preferablybe the same throughout the kiln. The spacing may thus vary for diierent parts of the kiln. For example in some places the space may be 1/2 inch, in others more or less than 1/2 inch; The firing temperature is quite important as'the use of too low a firing temperature brick. As already explained, the two types of hard flint clay require distinctly different tiring treatments.

The low burning type which is found most usually in the clay elds of Missouri should be fired at con 12, 13 or 14 (that is, between cones 12 and 14), while the high burning typewhich is found chiey in the diaspore ields of Missouri, though also present in some of the clay elds, should be red' at cone 16, 17 or 18 (that is, between cones 16 and 18) It is therefore necessary to identify the particular clay. This is preferably done by subjecting coarse lumps of the material to firing treatment at various temperatures, determining the bulk specic gravities In the work of Holmes and Paul, referred to above, no distinction was drawn between the high burning and low burning clays, and it is impossible to state with assurance which type was employed. The unsatisfactory results obtained may be attributable entirely to improper sizing, preparation and'molding, although it seems likely that improper ring treatment was also a factor.

The temperature chosen for firing should be a 'minimum of one pyrometric cone below the temperature at which the particular hard ilint clay attains its maximum bulk specific gravity.

. Improper firing treatment results in low bulk speciiic gravity, as obvious from the curves, low cold crushing strength and high reheat shrinkage.

The hard int clay .brick produced in accordance with the present invention show a number of distinctlydesirable properties. The alumina content of the nished brick is in excess of 42%, 'thus indicating that the brick is quite refractory.

The bulk specific gravity is. in excess of 2.38. The bulk specific gravity of the fired brick is in excess of 85% (preferably 90%) of the maximum bulk specific gravity attained by the calcined hard int clay as shown by the appropriate curve.

The brick exhibits a cold crushing strength, when determined by crushing a 9 x 45/2 x 21/2 inch brick on the 41/2 x 21A; inch faces, in excess of 1200 pounds per square inch (84.4 kilograms per square centimeter) and in the great majority of cases in excess of 1550 pounds per square inch (109 kilograms per square centimeter).

The linear shrinkage of the brick after reheating at 1 600" C. (2912 F.) for five hours is not more than 1% and in most cases vless than' 0.75%. This is to be compared with the linear reheat shrinkage of 2.1% obtained by Holmes and Paul at 2800* F. (1538 C.).

The spalling loss after preheatingto 1650 C. (about 3000 F.) is less than 1% in the brick of the present invention. y

The brick of the present invention exhibits a linear ring shrinkage of less than 9% in the ordinary case.

The manufacturing loss obtained in practicing the present invention is less than about 10%, which is a very favorable figure compared to usual int clay brick operations.

The above combination of properties makes the brick of the present invention entirely commercial and denitely superior to brick of the prior art manufactured from raw hard iiint clay or mixtures of raw and calcined hard hint clay.

Wherever percentages are mentioned in the present application, it will be understood that they are percentages by weight based upon the total dry ingredients or upon the dry brick, unless it is clearly indicated otherwise.

Wherever screensizes are mentioned it is understood that W. S. Tyler Standard Testing Sieves are meant. These screens have the following characteristics Mesh Opening Diameter of wire Millimeters Inches .M illmetcrs 263 6. 680 0. 070 1. 776 0. 131 3. 327 0. 036 0. 013 0. 093 2. 362 0. 032 0. 811 0. 0232 0. 589 0. 0125 0. 316 0. 0116 0. 295 0. 0092 0.233

, Whenever reference is made to linear change of brick after reheating at 1600 C. (2912 FJ, it is understood that the brick has been tested in accordance with the standard test procedure described in American Society for Testing Materials, Standard C-11336, schedule C, as it appears in A. S. T. M. Standards (1936) Part II, Non-Metallic Materials, pages 222-223inclusive.

Whenever reference is made to spalling loss of brick after preheating at 1650 C. (3002 F.) vit is understood that the brick has been tested in accordance with the tentative standard procedure described in American Society for Testing Materials, Standard C-122-36T as it appears in A. S. T. M. Tentative Standards (1936) pages 457-458 inclusive.

It will be evident that it is quite important, in practicing the present invention, to determine the ring properties of the particular hard ilint clay before attempting to manufacture it into brick. In making the brick, calcined clay material should be eliminated or kept below 5%, the hard iiint clay should be sized and combined as already explained and bonded with 2% to 5% of bentonite. 'Ihe mix should then preferably be prepared in a, special pan. The molding efciency should be in excess of 90% and the firing should be done at a minimum temperature of one pyrometric cone below the temperature producing the maximum bulk specific gravity of the hard flint clay as indicated by ring tests. As an indication of satisfactory iiring, the bulk specific gravity of the red brick should be in excess of (preferably of the maximum bulk specic gravity of the calcined hard flint clay.

of the benefits of our invention without copying the method or composition disclosed, and we,

therefore, claim all in so far as they fall within the reasonable spirit and scope of our invention. Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. The process of producing dense'refractory int clay brick, which comprises preparing a mix of between 30% and '10% of hard flint clay particles from 3 to 28 mesh per linear inch, between '10% and 30% of hard intclay particles below 48 mesh per linear inch and between 2% and 5% of bentonite, the int clay containing between 35% and 45% of alumina `and including not more than 5% of calcined clay materlal,molding the mix into brick under a molding eilicien'cy above 90% and ring the brick at a minimum temperature of one pyrometric cone below the temperature producing maximum bulk speciic gravity when ring lumps of the particular iiint clay, the burned brick when reheated at 1600 C. for ive hours showing a linear shrinkage not more than one percent. Y

2. The process of producing dense refractory int clay brick, which comprises preparing a mix of between 30% and '70% of hardint clay particles from 3 to 28 mesh per linear inch, between '70% and 30% of hard iiint clay particles below 48 mesh per linear inch and between 2% and 5% of bentonite, the flint clay containing between 35% and 45% of alumina and including not more than 5% of calcined material, molding the mix into brick under a molding eiiiciency above 90% and ring the brick at a temperature producing a bulk specic gravity of the fired brick above'85% of the maximum bulk specific gravity of red lumps of the int clay.

3. The process of producing dense refractory flint clay brick from high burning hard Missouri int clay, which comprises preparing a mix of between 30% and 70%Y of Missouri int clay particles from 3 to28 mesh per linear inch, between '70% and. 30% of high burning hard Missouri 48 mesh per linear inch and between 2% and 5% .ilint clay brick which high burning hard*` int cla51 particles below of bentonite, the int clay containing between A and of alumina and including not more than 5% of calcined clay material, molding the mix into brick under a molding eiliciency above 90% and ring the brick at a temperature between pyrometric cones 16 and 18, the burned brick when reheated at 1600 C. for ve hours showing a linear shrinkage of` not more than one per cent.

4. 'I'he process of producing dense refractory flint clay brick from low flint clay, which comprises preparing on a special` pan a mix of between 30% and '10% of low burning hard Missouriflint clay particles from 3 to 28 mesh per linear inch, between '70% and 30% of low burning hard Missouri flint clay particles below 48 mesh per linear inch and between 2% and 5% of bentonite, the int clay Vcontaining between 35% and 45% of alumina and including not more than 5% of calcined clay material,

burning hard Missouri molding the mix 'into brick under a'molding efciency above 90% and firing the brick at a temperature between pyrometric cones 12 and 14, the burned brick when reheated at 1600 C. for five hours showing alinear shrinkage of not more than one per cent. s

5. 'I'he process of producing dense refractory comprises preparing a mix of clay particlesv including more than of hard flint clay particles with between 2% and 5% of bentonite, the clayparticles containing not more thanl 5% of calcined clay material, molding the mix into brick'under a pressure in excess of 1,000 pounds per square inch and ring the brick to a temperature high enough to produce a brick which when reheated at 1600 C. for ve, hours shows a linear change not more than one per cent.

RUSSELL P. 

